1. Field of the Invention
The invention relates to a semiconductor device and a method of manufacturing the same, in particular, to a semiconductor device and a method of manufacturing the same relating to forming a wiring extending over a step portion near a dicing line from the lower surface to the upper surface of the step portion.
2. Description of the Related Art
In a process of manufacturing a semiconductor device, a pattern need be formed over various step portions such as a LOCOS (Local Oxidation of Silicon) step, a polysilicon wiring step, an aluminum wiring step and so on from the lower surfaces to the upper surfaces of these step portions by a photolithography process. In this case, since exposure light incident perpendicularly on a step portion is reflected obliquely, sometimes a pattern transferred on a semiconductor substrate does not correspond to a photomask pattern.
In a manufacturing line in which miniaturization is enhanced, a photoresist is mainly of a positive type. In a case of a positive resist, a reticle (photomask) of which a portion for forming a pattern on a semiconductor substrate is black is used, and the positive resist on the semiconductor substrate that is exposed to light perpendicularly entering through the transparent portion of the reticle is removed through a development process. The black pattern of the reticle is transferred on the semiconductor substrate.
In this case, light reflected at various step portions as described above existing on the semiconductor substrate may enter under the black pattern of the reticle and the photoresist in a portion that should not be exposed to light may be exposed to the light. The resist in the portion where light enters under the pattern to be transferred on the semiconductor substrate is also removed through a development process, resulting in forming a narrower pattern on the semiconductor substrate than a designed pattern or resulting in separation of the pattern in a worse case.
In a case of forming a large pattern by a design rule that does not need miniaturization on a semiconductor substrate, ordinarily, a positive type photoresist is not used and a negative type photoresist is used. In this case, a negative resist irradiated with light is hardened and a negative resist in a portion that is not irradiated with light is removed through a development process.
Therefore, even if a negative resist under a black pattern of a reticle is exposed to light reflected at a step portion, the width of the hardened negative resist only increases to form a protruding portion in the pattern, and separation does not occur in the pattern. Ordinarily, the increased width of the pattern does not cause a problem in a case of a non-miniaturized design rule.
As a method of preventing an abnormal pattern such as a narrowing or protruding portion from being transferred on a semiconductor substrate by light reflected at a step portion, covering a surface of an object to be exposed with a reflection preventing film, treating a photoresist material, and so on are disclosed in Japanese Patent Application Publication Nos. Hei 9-69479, Hei 9-211849 and 2005-072554.
In a case of forming an electrode pattern having high reflectance over a step portion formed on a semiconductor substrate from the lower surface to the upper surface, the probability that an abnormal pattern such as a narrowing portion is formed on the semiconductor substrate by light reflected at the step portion increases more. Such an abnormal pattern causes a problem usually when a miniaturized positive type photoresist is used. Japanese Patent Application Publication No. Hei 9-69479 and so on belong to this case.
Ordinarily, in a case of using a negative resist for a large pattern by a design rule, exposure light reflected at a step portion does not cause a serious problem since it only slightly enlarges a transferred pattern on a semiconductor substrate. However, there is a case that a positive resist is used even for a large pattern by a design rule. In a semiconductor device manufacturing line that uses a positive resist in almost all photolithography processes for miniaturized patterns, such a case occurs when a non-miniaturized pattern is to be formed only in a few processes.
In this case, although the pattern may be formed by using a negative resist, it is necessary to prepare two kinds of resist materials and two kinds of developers for each of a resist coating process and a resist development process, respectively, and there occurs a problem in material arrangement, material keeping, equipment keeping, a equipment operating ratio and so on. Furthermore, it is difficult to obtain a negative resist at low cost since a positive resist is mainly used nowadays.
Even in such a case of using a positive resist for a large pattern by a design rule, light reflected at a step portion may cause a problem.
This is in a case where a glass substrate 4 or the like is bonded on a semiconductor substrate 1 on which a first wiring 3 is formed on the front surface side near a dicing line S and the semiconductor substrate 1 is etched from the back surface side of the semiconductor substrate 1 to expose the back surface of the first wiring 3 as shown in FIGS. 5A and 13. In this case, a step portion D is formed, having a thickness of about 100 μm or more and having inclined surfaces from the back surface of the semiconductor substrate 1 to the back surface of the first wiring 3 formed on the front surface of the semiconductor substrate 1.
When a second wiring 8 connected to the back surface of the first wiring 3 and extending over this step portion D onto the back surface of the semiconductor substrate 1 is formed by using a positive type photoresist as shown in FIG. 8, light reflected at the step portion D may causes an abnormal narrowed portion 8a as shown in FIG. 2 in the second wiring 8 on the lower surface of the step portion D including a portion connected to the first wiring 3. When the narrowed portion 8a is formed in the second wiring 8 on the lower surface of the step portion D and thus the second wiring 8 is narrowed, the wiring resistance of the second wiring increases and disconnection occurs in an extremely worse case.
Therefore, when the second wiring 8 is formed over the step portion D existing near the dicing line S, it is necessary to prevent the second wiring 8 from having an abnormal narrowed portion 8a on the lower surface of the step portion D.